The test on Mount Ordeals isn't about beating your dark side. It's about accepting it exists and learning to move on. Cecil didn't just mysteriously get his paladin powers; he already had the potential and he needed to be told things were possible. Cecil started thinking like a paladin when he chose to defend Rydia, but Mount Ordeals made him learn to move on.

#2.

...and that's the reason why Kain takes so damn long; Kain can't forgive himself and would rather excise it than accept it.

#3.

Cecil never got a good night's sleep until he became a paladin; as a dark knight he kept getting nightmares of all the people he'd been forced to hurt in Baron's name. Doubly so for the destruction of the village of Mist. As a paladin he could atone, and so he forgave himself.

#4.

Both Dark Knight and Paladin classes are about sacrificing yourself; the reason why they're opposites is in the nature of the sacrifice. The former is about lending yourself to bloodlust, and that's why they talk about the potential for darkness to consume him if he continues down that path - after a while, it's all too easy to lose control and justify anything and everything you do, and not look back. The latter is a willing choice to intervene for the sake of others, because you recognise that there are things bigger than yourself; it's a choice to protect not just people, but ideals: "There is good in this world, and it is worth fighting for."

#5.

Some fight for law. Some fight for justice. Cecil fights for redemption: not always for himself, but for others as well, which is why the man is so forgiving.

Part of this is because he got a second chance, and so he feels the need to extend this to others; part of this is his personality, and part of this has to do with the nature of being a paladin.

#6.

Rosa wishes Cecil and Kain would just Figure It Out. She loves them both; they both love her - and each other - and things would be a lot easier on all of them if Cecil and Kain worked it out. Of course, because it's Cecil and Kain, they're not working it out and she has to engineer ways to get them to realise it. She's on the verge of just knocking their skulls together.

#7.

Kain was more of a mischief-maker than Cecil as a child. After they became friends, Kain got into less trouble partly because he wasn't picking fights with Cecil any more, and partly because Cecil was good at covering for him. Cecil never lied to cover up, because that would be dishonourable for them both. But he certainly didn't let Kain know, either, because Kain would've been upset.

#8.

The chamber on Mt. Ordeals isn't the entirety of the trial; the trial is what came before, and what comes after.

#9.

Cecil doesn't really know what or how a paladin's supposed to conduct himself; after all, he's the first, and he knows he's made a lot of mistakes in the past. So he does rely a great deal on Kain and Rosa's counsel - he always has, and he always will. Every time either of them isn't there, he feels vaguely lost.

That being said, when both of them weren't there, he had to learn to trust his own judgement. All part of the trial.